The Monster with 21 Faces

The Monster with 21 Faces (怪人21面相, Kaijin Nijūichi Mensō) was a name (based on Edogawa Rampo's fictional villain "The Fiend with Twenty Faces") used as an alias by the group responsible for the blackmail letters in the Glico Morinaga case in Japan, in 1984. Variations of the name's translation, including "the Mystery Man with the 21 Faces" and "the Phantom with 21 Faces", have also been used in articles and books featuring the case.

Source: Wikipedia — The Monster with 21 Faces (CC BY-SA 4.0)